The present invention relates to optical adjustment elements and their use for the precise concentric coupling of a monochromatic parallel beam of rays into an optical microscope. Two different but closely related forms of adjusting elements are disclosed.
For the intense punctiform illumination of microscopic specimens for photometric or spectroscopic examinations, for instance for the selective excitation of individual regions of the specimen for fluorescence or Raman analysis, it is already known to couple a laser beam into the illuminating system of an optical microscope which is focused, limited in refraction by the objective of the microscope, to a diameter of about 1 um in the object plane.
With such an arrangement, the optical axes of the microscope and the additional laser illuminating device must agree precisely. Lack of alignment of the axes leads to non-uniform illumination of the pupil of the objective, which makes itself perceptible in an undesired fanning out of the focus of the laser in the object plane.
During the operation of the laser, however, displacements and tiltings of the laser beam by small amounts take place in the course of a slow drift. The lack of alignment of the expansion optical system generally used which is arranged behind the laser is further increased by the expansion factor. It is thus necessary to provide adjustment means to compensate for the lack of alignment and the tilting of the laser beam with respect to the optical axis of the microscope.
As adjustment means for tilting of the axis, use may be made in known manner of deflection mirrors which are in any event possibly present in the path of the beam. However, it must be borne in mind that such adjustment mirrors as a rule introduce an additional defect in alignment, since the plane of the mirror, the axis of tilt of the mirror, and the optical axis of the laser do not always intersect precisely at one point.
From German Pat. No. 720,904, published May 19, 1942, it is furthermore known to use transparent wedges which are turnable independently of each other around the optical axis in order to adjust for tilting of the axis.
As adjustment means for parallel misalignment, it is possible to use so-called parallel-plate micrometers consisting of two plates of glass with planoparallel surfaces, the inclination of which can be varied with respect to the optical axis. Such an arrangement is disclosed in West German Pat. No. 1,094,485, published Dec. 8, 1960. Such an adjusting device has, however, the disadvantages that, on one hand, the transmission of the plates, even with extensive elimination of reflections, is dependent on angle, and that, furthermore, the adjustment mechanism, which possibly must contain a step-down gearing for fine adjustments, is relatively expensive.
The object of the present invention is to create an optical adjustment element for axial misalignment which is of relatively simple and inexpensive construction, and is convenient to handle.